Process and device for vaporizing electrically conductive substances, preferably metals, in vacuo



saw-121 H. WALTER 2,939,943 PROCESS AND DEVICE FOR VAPORIZING ELECTRICALLY METALS, IN VACUO Filed June 23, 1955 i I i CONDUCTIVE SUBSTANCES, PREFERABLY June 7, 1960 -ilnitccl States atent Patented June 7, 1960 PROCESS AND DEVICE FOR VAPORIZING ELEC- TRICALLY CONDUCTIVE SUBSTANCES, PREF- ERABLY METALS, IN VACUO Heinz Walter, Wiesbaden, Germany, assignor to VAC Anstalt, Vaduz, Liechtenstein, a company of Liechtenstein Filed June 23, 1955, Ser. No. 517,623

Claims priority, application Germany July 27, 1954 17 Claims. (Cl. 219-76) For the production of metal vapour in vacuo, for example for metallizing certain materials, the metal is con verted into the vapour state, for example from heated crucibles or, when the metal is combined with a particular carrier material, by direct heating. There are several disadvantages in this process. The vaporization which can be effected is relatively limited, the losses of metal, for example by deposition on the walls of the vacuum chamber, are relatively high and it is hardly possible to control the vaporization, for example spatially and quantitatively. Further, the vaporized metals may form undesired alloys with their carrier material, which may be simultaneously vaporized and reach the material to be metallized together with the metal to be vaporized, so that for example the quality of the metallizing may be much reduced.

It has now been found that all these disadvantages and deficiencies are removed in simple manner, when applying the method in which the substance to be converted into vapour form, for example a metal, is exposed in the liquid condition in vacuo to the action of radiant heat, if in accordance with the invention the liquid substance is exposed, preferably by means of a nozzle, in the form of mist or the like to the radiation of highly heated bodies in front of the nozzle mouth, also and preferably simultaneously to the action of an arc in this space, in such a way that the mist is converted into vapour, for example partly by the radiation of the conductive body and partly by the self-maintained arc. This process is distinguished in particular by high output, low metal losses, very great purity of the metallizing layer and further, for example, by the fact that carrier materials need not be used for the metal, etc., to be vaporized. Moreover it is, for example, advantageous that substances, such as aluminium, can be satisfactorily vaporized in large quantities and over a long period of time and can be satisfactorily applied by vaporization to any desired materials, for example travelling webs of textile, paper or the like.

A further and very surprising advantage of the process of the invention is that hurtful alloys are not produced on the, for example metallic, walls of the vacuum chamber. As has been found a sheath of the vapour of the same substance is formed around a mist particle as it approaches the walls, perhaps by the Leidenfrost phenomenon; this sheath stops the metallic nucleus, which could form an alloy, from reaching the walls. The hot walls make condensation thereon impossible. In the present case the hot walls have the further effect that the metal vapour is forced to issue from the openings provided for the purpose in the chamber and to reach the material, for example a paper web, which is to be treated with the vapour. This outer space is preferably also kept under vacuum, so that the metal vapour particles issuing from the vaporization chamber fly to their target with practically uniform velocity and in a straight line.

The uniform vapour pressure within the vaporization chamber in combination with the high vacuum prevailing therein has the advantageous effect that the metal vapour fills the chamber fully and uniformly in the same way as the gas in a lighting tube filled, for example, with neon. Preferably in accordance with the invention, when an arc is employed, the, for example metallic, mist or spray jet produced by the nozzle is driven axially into the are maintained between at least two electrodes from one end of the arc.

The electrodes and the radiating conductive bodies preferably define a common space for the effective radiation of these bodies and for the are or arcs. This produces in particular a properly-closed operating space of relatively very small dimensions. The space in which the arc burns is preferably an elongated tube, at the end faces of which the electrodes maintaining the are through the chamber space are arranged. The one, two or more injection nozzles are preferably also provided at one or both end faces. The walls of the tube contain openings, for example slots, for the withdrawal of the metal vapour, which is applied outside as a vapour to the material to be metallized, for example to a paper web passed directly over the outside of the slot.

The walls of the chamber, when they consist of appropriate material, can themselves serve as an emission source for the heat energy and/or the electrons. It is also possible, however, to cover the interior of the walls wholly or in part with a special emission layer. The latter has for example the advantage that the direction and intensity of the emissions can be influenced in particularly simple manner, for example by making the layer of variable thickness or profiling, grldding or roughening the layer and/ or by not coating individual parts, for example definite strips, with the emission layer.

The walls or the emission layer disposed thereon are preferably heated to such a high temperature, for example to 2,000 C., that the resultant radiation reliably, completely and rapidly converts a large part or the whole of the mist, which consists for example of metal particles, into the vapour form.

The walls and if desired the layer thereon can be electrically heated, for example by direct or indirect heating, by induction or the like; in the last-mentioned case a metallic wall can form a part of the electrical circuit or field.

The are, which likewise serves for the conversion into vapour form of the mist, consisting for example of metal particles, which mist comes from a nozzle or, for example, from a crucible, should take such a course and be so strong that it where necessary itself reliably converts into the vapour state all mist particles not affected by the radiation from the walls or the emission layer thereon.

The liquid metal which is continuously brought into the arc chamber, advantageously in the form of a sharply limited jet, but generally better in the form of a spray, shower or mist, is preferably sprayed in by means of a nozzle or in atomized form. The nozzle is preferably adjustable,for example in such a way that it is possible to produce at will for example sharply limited jets, Wide spray cones or intermediate forms. The liquid metal or another electrically conductive substance to be vaporized should always be converted into the smallest particles by the nozzle.

The nozzles are preferably heatable and/or coolable. The heating is advantageously electrical, for example by means of a helical conductor surrounding the nozzle, whilst corresponding passages in the nozzle body itself are advantageous for cooling.

In place of one nozzle two or more nozzles can be provided. in which case it is advantageous so to arrange them that the spray streams unite spatially in predetermined manner. For example the jets or spray cones may run in the same direction or may cross or may run in opposite directions. If desired a combination of these forms may be advantageous, for example to subject as far as possible the whole of the space of the vaporization chamber to the action of the nozzles which may for example be controllable.

In many cases it is sufficient to vaporize the liquid metal, etc., from a crucible in which it rests, under the action of the hot Walls of the chamber which prevent condensation, of the appropriately high vacuum and of the electrical field between at least two electrodes capable of forming an are.

For the formation of the electrical field, for example the electrical field serving to strike and maintain the are, two special electrodes can be used. It is also possible, however, instead for example of one of these electrodes, to use the correspondingly conductive, for example metallic, wall of the chamber. When special electrodes are used, such an electrode is preferably associated with at least one nozzle, for example at one end face of the, for example cylindrical, chamber; the metal vapour can then issue from the opposite end face of the chamber which is not provided with nozzle and electrode.

The special electrodes advantageously each have the shape of a ring, which can be provided with cooling pas sages and electrical heating conductors. The field in the free space of these annular electrodes should so run and be so great that it forms a kind of invisible boundary wall for the metallic mist particles and vapour particles. In this way it is possible completely to close a tube which serves as the vaporization chamber and is open at both end faces by means of annular electrodes arranged on the outside in front of the end faces.

The vapour is withdrawn, for example through openings, for example slots in the tube wall running parallel to its axis or helically, and is passed into a further vacuum chamber where it strikes the material to be vapour-treated, for example a paper web. The slots or the like are preferably provided on the outer side of the tube with guide members which are preferably so constructed that they act like nozzles and suck the vapour out of the chamber. If desired special pumps, for example suction pumps, can be provided instead of or in addition to such guide members. The outlet openings should be variable, so that by means of them alone or by means of them together with a suction pump or the like the partial pressure of the, for example metallic, vapour and/or air prevailing within the vaporization chamber can be adjusted; the vapour pressure should be so high that a strong are always burns.

If the heatable metallic walls of the chamber are simultaneously used as a main or auxiliary electrode, the latter preferably receives a polarity which is opposite to the polarity of the electrode arranged near the injection nozzle. Preferably the nozzle and the associated electrode receive a positive polarity, Whilst the metallic periphery of the chamber and the other special electrodes receive a negative polarity. The nozzle is advantageously connected via a switch, which is opened as soon as the arc has struck. This prevents the nozzle from serving as an arc electrode and being exposed to the very great heat and other influences of the arc.

The electrodes and if desired the inner surface of the metallic walls of the chamber and the nozzle can be provided in part with electrically non-conductive or poorly conductive coatings for the formation of predetermined electrical fields or for the corresponding influencing of the electrical fields.

Further features of the invention are illustrated with reference to the embodiments of the invention shown in the annexed drawings, in which Fig. 1 is an axial section through an arrangement with two annular electrodes,

Fig. 2 is an axial section through an arrangement with only one annular electrode and Fig. 3 is a transverse section through an arrangement 4 with four nozzles displaced by with respect to one another.

From a spray nozzle 1 with a, for example electric, heating device 2 the liquid metal, for example aluminium, is so atomized into the chamber 3 which serves to a certain extent as a furnace that the metal enters the chamber in the form of a fine mist 4. The chamber consists of a heatable, preferably metallic, tube 5 the periphery of which is covered with emission layers 6. Preferably the tube is screened externally, Wholly or in part with sheet metal radiation shields, not shown, or the like. The metal vapour is withdrawn through the slit 7.

In front of the end faces 8, 9 of the tube are arranged the annular electrodes 10, 11, which are provided with an annular passage, for example 12, through which heating or cooling media can be passed. The field may be made so strong that it forms an invisible boundary wall for the metal mist and the metal vapour. The internal diameter of the tube 5 is preferably somewhat larger than the external diameter of the electrodes 10, 11. The mouth of the nozzle 1 is surrounded by the annular electrode 10. The electrode 10 and, via the lead 14 and switch 15, also the nozzle 1 are connected to the positive pole 16, whilst the electrode 11 and the metal tube 5 are connected to the negative pole 17, 18; the electrical connection of the tube 5 permits the supply of energy to the particles of the metal mist.

In the embodiment according to Fig. 2, in front of one end face of the cylindrical tube 5 which is open at both ends and forms the vaporization chamber 3 and is coated internally with the heat-radiating layer 6, there is arranged the annular electrode 10, behind which is disposed the centrally arranged nozzle 1, from which the liquid metal is driven as a mist 4 or as a jet (not shown) into the are burning in the chamber. The are is maintained between the electrode 10, which is connected to the positive pole just like the nozzle 1, which is connected via the switch15, and the tube 5 which is connected to the negative pole 13 and is highly heated and emits electrons into the metal mist and vapor which fills the chamber completely and uniformly. The vapour emerges from the completely open end face 19 of the tube.

In the embodiment shown in Fig. 3 the nozzles 1, 20, 21 and 22 are displaced by 90 with respect to one another and are also so arranged that the spray cones or the like 23, 24, 25, 26, cross in the chamber 3. In this case also the chamber is filled fully and uniformly with mist and vapor.

The process according to the invention takes place, for example, when using the above-described devices in that the electrodes 10 and 11 are brought to striking potential and after closing the switch 15 the liquid metal, for example aluminium, is sprayed from the nozzle 1 into the chamber 3 whereby a fine metal mist is produced. The electrons and heat rays emitted by the highly heated tube 5 or its emission layer 6 convert at least a major part of the mist particles into vapour; the emission is intensified when the tube 5 is at a negative potential. Due to the vaporization of metallic mist particles an arc is struck between the electrode 10 on the one hand and sleeve 5 and electrode 11 on the other, which are penetrates the mist and itself contributes to the conversion of the mist particles into vapour.

In order to protect the nozzle 1 the switch 14 is preferably opened immediately after the arc has struck so that the nozzle no longer serves as an electrode and the are consequently remains free.

In the chamber 3 the metal vapour produced builds up to a predetermined vapour pressure which is adjustable, for example, by means of the outlet opening 7.

What I claim is:

1. Apparatus for the conversion of electrically conductive substances, into vapor in vacuo, comprising heating means for the liquefaction of the substance to be converted into vapor, nozzle means for atomizing the resulting liquid substance to mist form, a vaporization chamber wherein vacuum is maintained, said chamber having walls adapted to radiate heat and electrodes in the range said vaporization chamber adapted for maintaining an arc, whereby the mist produced by said nozzle means is converted to vapor form in part by radiation from said radiating Walls and in part by the action of the vapor discharge caused by the are maintained by said electrodes.

2. Apparatus as in claim 1, wherein said electrodes and said vaporizing chamber walls bound the vaporization space within said chamber.

3. Apparatus as in claim 1, wherein at least one of said electrodes is disposed in the path of the mist projected by said nozzle means.

4. Apparatus as in claim 3, wherein said electrode is constructed in annulus form and surrounds the outlet of said nozzle means.

5. Apparatus as in claim 3, wherein said nozzle means is also an electrode.

6. Apparatus as in claim 5, wherein said nozzle serving as an electrode is disposed connectably to and separably from a further electrode.

7. Apparatus as in claim 1, wherein there is disposed at least one electrode in the path of the mist projected by said nozzle means and at least one second electrode in the axially opposite part of said vaporization chamber.

8. Apparatus as in claim 7, wherein one electrode is constructed in an annular form and wherein the electric field serves as a shield for the mist, separating said mist from said vaporization chamber.

9. Apparatus as in claim 1, wherein at least one electrode is disposed in the path of the mist projected by said nozzle, and conducting walls of said vaporization chamber form a further electrode.

10. Apparatus as in claim 1, wherein the electrodes are coated with poorly conducting coatings for the purpose of correspondingly influencing the electric fields of said electrodes.

11. Apparatus as in claim 1, wherein the vaporization space is confined to one part of said vaporization chamber by means of solid walls, and to another part thereof by means of an electric field produced by said electrodes.

12. A process for the conversion of electrically conductive substances into vapor form in vacuo, comprising transforming the substance into the liquid state, atomizing the liquid substance to mist form, and subjecting the atomized liquid substance to the radiation of highly heated bodies and an electric arc to convert the atomized liquid substance to vapor.

13. Apparatus for the conversion of electrically conductive substances, into vapor in vacuo, comprising heating means for the liquefaction of the substance to be converted into vapor, nozzle means for atomizing the resulting liquid substance to mist form, a vaporisation chamber wherein vacuum is maintained, said chamber having walls being adapted to radiate heat and carrying an emission layer, and electrodes in said vaporisation chamber adapted for maintaining an arc, whereby the mist produced by said nozzle means is converted to vapor form in part by radiation of said radiating walls and in part by the vapor discharge caused by the are maintained by said electrodes.

14. Apparatus for the conversion of electrically conductive substances into vapor in vacuo, comprising heating means for the liquefaction of the substance to be converted into vapor, a plurality of nozzles for atomizing the resulting liquid substance to mist form, said nozzles being so disposed that the spray streams produced thereby unite spatially in a predetermined manner, a vaporization chamber wherein vacuum is maintained, said chamber having walls adapted to radiate heat, and electrodes in said vaporisation chamber adapted for maintaining an arc, whereby the mist produced by said nozzles is converted to vapor form in part by said radiation of said radiating walls and in part by the action of the vapor discharge caused by the are maintained by said electrodes.

15. Apparatus for the conversion of electrically conductive substances in to vapor form in vacuo, comprising heating means for the liquefaction of the substance to be converted into vapor, nozzle means for atomizing the resulting liquefied substanceto mist form, a vaporization chamber wherein vacuum is maintained, said chamber having walls adapted to radiate heat, electrodes in said vaporization chamber adapted for maintaining an arc, whereby the mist produced by said nozzle means is converted to vapor form in part by radiation from said radiating walls and in part by the action of the vapor discharge caused by the are maintained by said electrodes, said chamber walls having therein at least one slit-formed aperture for connection with a vacuum chamber adapted to receive objects to be coated by mist formed in said vaporization chamber.

16. Apparatus as in claim 15, wherein the outlet apertures are changeable in their magnitude.

17. Apparatus as in claim 15, wherein the slit formed aperture is in one end of said vaporization chamber, and said nozzle means at the other end thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,281 Sommer Mar. 16, 1937 2,169,981 OBrien June 6, 1939 2,373,639 Turner Apr. 10, 1945 2,416,211 Osterberg Feb. 18, 1947 20,722 Peterson May 20, 1947 2,643,201 Chadsey June 23, 1953 2,752,882 Heimann July 3, 1956 2,754,225 Gfeller July 10, 1956 FOREIGN PATENTS 483,517 Great Britain Apr. 21, 1938 OTHER REFERENCES "Vaporized Metal Coatings, published by Distillation Products, Inc. (Rochester 13, N.Y.) (1949) (page 9 relied on). 

